This invention relates to dry type developing devices, usable with various types of image formation apparatus, for developing an electrostatic latent image, an electric potential latent image, a magnetic latent image or the like.
Of the various electrostatic printing techniques, the most familiar is that of xerography wherein latent electrostatic images formed on a charge retentive surface are developed by a suitable toner material to render the images visible, the images being subsequently transferred to plain paper.
A less familiar form of electrostatic printing is one that has come to be known as direct electrostatic printing (DEP). This form of printing differs from the aforementioned xerographic form, in that, the toner or developing material is deposited directly onto a plain (i.e. not specially treated) substrate in image configuration. This type of printing device is disclosed in U.S. Pat. No. 3,689,935 issued Sep. 5, 1972 to Gerald L. Pressman et al.
Pressman et al disclose an electrostatic line printer incorporating a multilayered particle modulator or printhead comprising a layer of insulating material, a continuous layer of conducting material on one side of the insulating layer and a segmented layer of conducting material on the other side of the insulating layer. At least one row of apertures is formed through the multilayered particle modulator. Each segment of the segmented layer of the conductive material is formed around a portion of an aperture and is insulatively isolated from every other segment of the segmented conductive layer. Selected potentials are applied to each of the segments of the segmented conductive layer while a fixed potential is applied to the continuous conductive layer. An overall applied field projects charged particles through the row of apertures of the particle modulator and the density of the particle stream is modulated according to the pattern of potentials applied to the segments of the segmented conductive layer. The modulated stream of charged particles impinge upon a print-receiving medium interposed in the modulated particle stream and translated relative to the particle modulator to provide line-by-line scan printing. In the Pressman et al device the supply of the toner to the control member is not uniformly effected and irregularities are liable to occur in the image on the image receiving member. High-speed recording is difficult and moreover, the openings in the printhead are liable to be clogged by the toner.
U.S. Pat. No. 5,040,004 granted to Frederic W. Schmidlin on Aug. 13, 1991 relates to a direct electrostatic printing apparatus including structure for delivering developer/toner particles to a printhead forming an integral part of the printing device. The developer/toner delivery system insures even distribution to an apertured printhead structure. To this end, toner is deposited on a donor belt using a magnetic brush structure. The belt is entrained about a drive roller and an idler roller as well as a stationary mandrel. The mandrel is positioned opposite the printhead structure with a portion of the belt disposed intermediate thereof. The mandrel is provide with a flat area which is coplanar with the printhead structure. The flat area is coextensive with the space occupied by a plurality rows of apertures in the printhead to thereby provide a uniform spacing between each row of apertures and the toner delivery belt.
U.S. Pat. No. 4,460,267 issued on Jul. 17, 1984 relates to a developing device mountable into and demountable from an image formation apparatus. It includes a housing provided with an aperture, a shutter assuming a position to close the aperture when the device is mounted in the image formation apparatus, and a position to open the aperture when the device is not mounted in the image formation apparatus.
U.S. Pat. No. 4,647,180 issued on Mar. 3, 1987 discloses a developing device constructed so that a developing agent resupply section is located side by side with a developing chamber, and a feed member for feeding a developing agent into the developing chamber is disposed in the developing agent resupply section.
U.S. Pat. No. 4,607,939 issued on Aug. 26, 1986 discloses a removable developing unit of an electrostatic recording apparatus, particularly a multi-color copying apparatus, having a casing with an aperture, at one side to allow contact of a developing sleeve with a photoconductive member when the developing unit is mounted in the copying apparatus. A cover and an automatic closing mechanism is provided so that the aperture is covered when the developing unit is removed from the copying apparatus. The casing includes a toner hopper to which a replaceable toner cartridge is attached. The correct color of replacement toner for the developing unit is ensured by removable tabs or openings on the toner hopper which matches those of the correct color toner cartridge.
U.S. Pat. No. 4,212,264 issued on Jul. 15, 1980 discloses an apparatus for supplying electrophotographic developer to an electrophotographic developing device is disclosed. The developer supply apparatus includes a cartridge containing therein an amount of developer and supported within the housing of the supply apparatus in a manner that the cartridge is allowed to move rotationally and reciprocally around and along its axis. The cartridge has an opening at its one end and also a plural number of ribs provided within the cartridge. During the movement of the cartridge, the ribs stir the developer contained in the cartridge and also cause the developer to move toward the opening. The cartridge is brought into motion responding to a supply signal so as to effect a supply of developer from the cartridge to the developing device.
U.S. Pat. No. 4,583,832 issued on Apr. 22, 1986 discloses developing device adapted to be removably mounted with respect to an image forming apparatus, there are provided protective cover members for covering and protecting a developing sleeve for developing a latent image on an image bearing member and spacer rollers for maintaining the gap between the image bearing member and the developing sleeve at a predetermined distance. Opening/closing of these protective cover members is effected in response to operation of a member such as a handle which is capable of being drawn out with respect to the developing device.
Toner belt type development systems similar to the ones discussed above are normally contact devices configured to operate in the machine process direction to avoid image smear. This given parameter establishes a toned belt width of at least nine inches to accommodate a minimum 8.5.times.11 inch copy sheet and increases with paper size and feed direction. The belt circumference can become substantial as it is most often designed to accommodate its toner supply system. Such developer systems must also accommodate the rolls required for belt tracking, and for driving and for supporting the belt for movement in the copier or printer. Due to the problem of belt tracking in a toner environment, part count, cost and a limited need for such a system, donor belt mechanisms have not been used extensively in present copier/printer applications.
Future and present machines considering non-contact jumping toner development that may require color capability in a confined space, with high reliability, and special applications such as Direct Printing may require the features provided by the present invention.